The long term goal of this project is to understand the biomechanical functions of the cruciate ligaments through an extensive and detailed study of the forces generated in these important structures. A series of controlled loading tests will be performed on fresh cadaveric specimens to identify the applied knee forces and moments which generate high cruciate ligament forces. Knowledge of cruciate ligament forces (and the types of knee loadings which produce them) is important in identifying and understanding mechanisms of injury, and for formulating recommendations for post-operative sports activities and rehabilitation exercises which will limit forces generated in a ligament which has undergone repair, augmentation, or substitution. The effects of graft pretension on the forces developed in an ACL substitute are important for developing protocols for optimum surgical implantation. In preliminary work, a new and unique experimental technique has been developed for the direct measurement of the resultant ACL force in cadaver specimens. This technique involves mechanical isolation of a bone plug containing the ACL's tibial insertion, and fixation of this bone plug into a specially designed miniature load cell which measures the three components of ACL force as external loads are applied to the tibia. The resultant force and its direction of pull are calculated and stored using a computerized data acquisition system. For this project, both the ACL and PCL will be instrumented and specific straight loading tests (under defined test conditions) will be performed including: passive flexion/extension, applied AP tibial force, applled internal/external tibial torque, and applied varus-valgus bending moment. Combined loading tests will consist of selected combinations of the above straight loading modes. The specific aims of this investigation are as follows: 1. Forces in the PCL will be measured during a series of straight and combined loading tests. 2. The effect of detaching one cruciate ligament upon the force developed in the remaining cruciate ligament will be determined. 3. The relationship between localized ligament strains (as measured by implanted Hall effect transducers) and total ligament force (as recorded by the cruciate load cells) will be determined. 4. The effects of combined section of the posterolateral structures (lateral collateral ligament + popliteus tendon + arcuate complex) upon the force generated in the posterior cruciate ligament will be studied. 5. The relationship between graft pretension and the force developed in a cruciate ligament substitute will be studied.